Driving Recursive Dehydration by PIII/PV Catalysis: Annulation of Amines and Carboxylic Acids by Sequential C-N and C-C Bond Formation.

A method for the annulation of amines and carboxylic acids to form pharmaceutically relevant azaheterocycles via organophosphorus PIII/PV redox catalysis is reported. The method employs a phosphetane catalyst together with a mild bromenium oxidant and terminal hydrosilane reductant to drive successive C-N and C-C bond-forming dehydration events via the serial action of a catalytic bromophosphonium intermediate. These results demonstrate the capacity of PIII/PV redox catalysis to enable iterative redox-neutral transformations in complement to the common reductive driving force of the PIII/PV couple.